In semiconductor wafer substrate (wafer) cleaning, particle removal is essential. Particles can be removed by chemical means or by mechanical means. In current state of the art, particles are usually removed by both a combination of mechanical means and chemical means. The current state of the art is to immerse a wafer into a bath filled with a liquid and to apply high frequency (megasonic) irradiation to the liquid. The sonic waves travel through the liquid and provide the mechanical means to remove particles from the wafer surface. At the same time, chemicals in the liquid provide a slight surface etching and provide the right surface termination, such that once particles are dislodged from the surface by the combination of etch and mechanical action of the sonics on the particles, these particles are not redeposited on the surface. In addition, chemicals are chosen such that an electrostatic repulsion exists between the surface termination of the wafer and the particles.
Wet etching and wet cleaning of wafers is usually done by immersing the wafers into a liquid. This can also be done by spraying a liquid onto a wafer or a batch of wafers. Wet wafer cleaning and etching is traditionally done in a batch mode. Because of the need for a shorter cycle time in chip manufacturing, there is a need for fast single wafer processing. Single wafer processing is usually limited to one side of the wafer. When cleaning wafers, it is important to clean both sides of the wafers at the same time.
It is also important to keep the wafer wet during transport from a wet cleaning chamber to a drying chamber so as to prevent dry residue deposits.